Seeing ice In the photo series shown in “Taking Antarctica’s temperature”(SN: 7/27/13, p. 18), the ice appears to be increasing from January to April as one would expect in the Southern Hemisphere. How does this demonstrate the rapid collapse of the Larsen B Ice Shelf?William Meadows, Dripping Springs, Texas

The satellite images show a large area of the Antarctic Peninsula; the Larsen B Ice Shelf is a small area near the center. A closer view of Larsen B (above) from March 7, 2002, reveals that what looks like a solid sheet of ice in the wider view is actually composed of thousands of icebergs that have broken free. — Editors

The length of human pregnancy varies naturally by five weeks, researchers have found. A new study followed 125 women from conception to live single births and found the longest pregnancies in women who were older, had previously had long pregnancies or were themselves heavier at birth.

Many parents have questions about how to raise children “naturally.” When is the natural time to wean a baby? Is early toilet training natural? What about suggestions to eat the placenta?

Martin, a primatologist, looks to evolutionary history for clues to how humans have parented through time. He leads a dizzying tour through evolutionary aspects of human reproduction, starting with sperm and egg, winding through pregnancy and parental care, to reach the decidedly unnatural topics of contraception and in vitro fertilization.

Stories of heroes are all over the news: First responders and even concerned passersby put themselves in harm’s way to help others, going against every instinct for self-preservation. What could explain such selfless acts? Even Charles Darwin struggled to understand the evolutionary upside of self-sacrifice.